Particle system domain box deforms the character (smoke effect)
Your rig object has a non-uniform scale, giving the character a squished appearance.

To fix this, clear the keyframes on the scale (as the scale doesn't actually change, this won't affect the appearance of the animation), then copy the X or Y value to the Z value:



This shouldn't have been caused or otherwise had anything to do with the smoke simulation. Perhaps you may have accidentally changed the scale while Auto keyframe was enabled (as it is in your screenshot)?